Sorry, I can't explain it, but I can tell you last year I did a series of expensive and completely useless promos via FB. Again, apparently thousands and thousands of people clicked on the ad and less than .001% bought a copy. My problem is I find it hard to trust the figures they throw up. They could just as easily put 50k and who's to dispute it?
Incidentally, I also ran ads via Goodreads and had a few hundred people add my book to their TBR lists, but I couldn't tell you how many of those actually became sales. I'm guessing very few, especially considering many of those people already had thousands of books they were waiting to read. My best experience with ads came from Bookbub, but the catch there is the price of your book has to be knocked down (usually to .99 cents) and even then I only made thirty of forty bucks in profit. So it was good, but not great.
Incidentally, I also ran ads via Goodreads and had a few hundred people add my book to their TBR lists, but I couldn't tell you how many of those actually became sales. I'm guessing very few, especially considering many of those people already had thousands of books they were waiting to read. My best experience with ads came from Bookbub, but the catch there is the price of your book has to be knocked down (usually to .99 cents) and even then I only made thirty of forty bucks in profit. So it was good, but not great.